Search

Chang'e-3(CE-3) has been the first spacecraft to soft-land on the Moon since the Soviet Union's Luna 24 in 1976. The spacecraft arrived at Mare Imbrium on December 14, 2013 and the same day, Yutu lunar rover separated from lander to start its exploration of the surface and the subsurface around the landing site. The rover was equipped, among other instruments, with two Lunar Penetrating Radar systems (LPR) having a working frequency of 60 and 500 MHz. The radars acquired data for about two weeks while the rover was slowly moving along a path of about 114 m. At Navigation point N0209 the rover got stacked into the lunar soil and after that only data at fixed position could be collected. The low frequency radar data have been analyzed by different authors and published in two different papers, which reported totally controversial interpretations of the radar cross sections. The present study is devoted to resolve such controversy carefully analyzing and comparing the data collected on the Moon by Yutu rover and on Earth by a prototype of LRP mounted onboard a model of the CE-3 lunar rover. Such analysis demonstrates that the deep radar features previously ascribed to the lunar shallow stratigraphy are not real reflectors, rather they are signal artefacts probably generated by the system and its electromagnetic interaction with the metallic rover.

We propose a strategy to evaluate the performance of a radar sounder for the subsurface exploration of the Europa icy crust and, in particular, the possibility to detect liquid water at the base of the ice shell. The approach integrates the information coming from experimental measurements of the dielectric properties of icy materials, thermal models related to different crustal scenarios, and numerical simulations of radar signal propagation. The radar response has been evaluated in terms of cumulative attenuation, signal-to-noise ratio (SNR), and reflectivity. Our simulations indicate that a subsurface radar operating at 9 MHz can identify shallow-buried targets and to detect the ice/water interface in various thermal scenarios. Under our assumptions the ice/water interface can be detected almost down to a depth of 15 km under a conductive ice shell, whereas for a convective ice shell, the maximum depth is about 12 km (in the cold downwelling plume). We also discuss the possibility to detect shallow targets associated with interfaces between pure water ice and $\text{MgSO}_{4} \cdot 11 \text{H}_{2}{\rm O}$ ice mixtures at various salt contents, using the data of laboratory dielectric measurements.

This paper presents the results of a ground penetrating radar (GPR) survey conducted in the rural area of the ancient city of Ferento near Viterbo (Northern Latium, Italy), where the visible ruins testify an uninterrupted history from the Etruscan to the Medieval period. The soil covering the ruins has been intensively ploughed, cultivated and used for pasture over the centuries, and is characterised by a high content of clay minerals. In this scenario, the use of GPR is particularly difficult due to both possible ‘false positive anomalies’ and strong signal attenuation. In order to reconstruct the geometrical shape and size of the geophysical anomalies related to a medieval dwelling, multi-profile GPR data were collected in two different areas, using radar equipped with 250-MHz antennas. 2D and pseudo-3D migrated maps were created and signal velocity analysis was performed to estimate the target depths. Despite the clayey-calcareous material, the results show a good signal penetration and allow a clear reconstruction of the shape of the buried ruins, confirming that the anomalies are due to medieval buildings located at a depth in agreement with what was observed on the archaeological stratigraphy. Furthermore, our study suggests that in radar data interpretation, caution should be used if the surveyed area was subjected to prolonged and intensive agriculture.

One of the main objectives of proposed missions to the icy Jovian moons is to prove the existence of the postulated subsurface ocean on Europa using radar sounders. The success of these missions will rely on the ability of the radar signals to penetrate ten kilometers of icy material that could potentially contain various types of impurities. In this work we quantify the impact of magnesium sulfate hydrates on the electrical properties of water ice by performing a series of dielectric measurements on different ice/MgSO4⋅11H2O mixtures as a function of frequency and at temperatures comparable with those expected on the icy satellite surfaces. Our results indicate that the salt only affects the real part of permittivity of the mixtures, whereas the imaginary part, hence the attenuation, does not significantly differ from that of pure ice. This means that in some regions signal penetration may be better than previously thought.

Recently, various studies have been carried out in order to address the possible relationships between amplitude attributes of the “first-arrival direct wave” (the so-called “early-time signal,” ETS), propagating at the interface in bistatic ground-penetrating radar (GPR) configurations, and the relevant shallow-soil permittivity parameters (dielectric constant and conductivity). In this frame, ad hoc compared numerical analyses and experimental investigations are extensively developed and discussed here, with the aim of making clearer the distinctive features and the reliability of this technique. The accurate results achieved for the ETS behavior as a function of various GPR system parameters enable us to identify both which are the more revealing signal attributes able to give predictable correlation with the ground permittivity values and the degree of complexity of the functional relationships between ETS amplitude and system parameters. A number of indications and perspectives are, thus, outlined in order to elucidate features, potential and critical aspects of the ETS technique for effective geophysical applications.

"Several factors affect antenna-soil coupling in a Ground Penetrating Radar (GPR) survey, like surface. roughness, lithology, lateral heterogeneities, vegetation, antenna height from the surface and. water content. Among them, lithology and water content have a direct effect on the bulk electromagnetic. properties of the material under investigation. It has been recently pointed out that the wavelet. of the early-time portion of a radar signal is correlated to the shallow subsurface dielectric properties. of a material. This result indicates that some information on such properties can be directly. extracted from the analysis of GPR early-time traces.. In the present paper, we use the early-time GPR signal, in terms of average envelope amplitude. computed on the first half-cycle, to map the near-surface (few centimetres) lateral distribution of. dielectric parameters, induced by changing the shallow water content on a concrete slab. This controlled. experiment was specifically designed to study the effect of water content variations on. antenna-material coupling, minimizing the influence of both surface roughness and heterogeneity.. The quantitative control of the water in the shallow portion of the slab is performed by using a portable. unilateral Nuclear Magnetic Resonance (NMR) sensor, which is able to determine the water. content in the material on the basis of the measured proton density. The results show a matching. pattern of the physical parameters measured with the two different techniques and a very high. degree of linear correlation (r = 0.97) between the radar early-time signal average amplitude and the. intensity of the NMR signal, which is proportional to the proton density, i.e., to the water content.. This experiment suggests that the early-time approach could be used as a fast and high- spatial. resolution tool for qualitatively mapping water content lateral variations in a porous material at. shallow depth, using a ground-coupled single-offset antenna configuration and that a quantitative. evaluation of the moisture content would require a calibration procedure."

We explore a new approach to evaluate the effect of soil electromagnetic parameters on early-time ground-penetrating radar (GPR) signals. The analysis is performed in a time interval which contains the direct airwaves and ground waves, propagating between transmitting and receiving antennas. To perform the measurements we have selected a natural test site characterized by very strong lateral gradient of the soil electrical properties. To evaluate the effect of the subsoil permittivity and conductivity on the radar response we compare the envelope amplitude of the GPR signals received in the first [Formula: see text] within [Formula: see text]-wide windows, with the electrical properties ([Formula: see text] and [Formula: see text]) determined using time-domain reflectometry (TDR). The results show that the constitutive soil parameters strongly influence early-time signals, suggesting a novel approach for estimating the spatial variability of water content with GPR.

The martian shallow crust has been studied through two subsurface sounding radars, MARSIS and SHARAD which operate at 3-5 and 20 MHz, respectively. The capability of radar to resolve the subsurface structures and the stratigraphy relates both on the radar features and the electromagnetic parameters of the shallow crust. For small grain size sediments, like clay minerals, the dielectric properties strongly affect the penetration depth of the radar signal. In this study, we measured several clayey samples, collected from various geological settings, with different mineralogy and water content using a Vector Network Analyzer (VNA) in the frequency range 1MHz-6GHz. The electrical properties were estimated as a function of temperature (200-298K) via the Nicolson-Ross-Weir algorithm using a coaxial-cage probe connected to the VNA. These measurements are used to interpret radar data in terms of depth penetration and surface echoes strength which could be affected by the temperature diurnal variation of martian surface.

The icy crusts of the Galilean satellites of Jupiter are supposed to be one of the potentially habitable zones of the solar system, and subsurface water oceans are believed to lie beneath them. The ice penetrating radar sounder RIME (Radar for Icy Moon Exploration) housed on board the JUICE (JUpiter ICy moons Explorer) mission is expected to probe the icy crust of Europa, Ganymede and Callisto up to a depth of about 9 km. The main objectives of RIME are: the characterization of the ice shell of Ganymede; the detection of melt materials inside the Europa's ice shell; the determination of the regolith thickness on Callisto. The penetration of the radar signal is strictly connected to the electromagnetic properties of the ice, that in turn depends on the presence of contaminants and temperature profile inside the satellite's crust. Laboratory measurements carried out in the temperature range of (100-273)K provided the dielectric properties of pure and doped ice (salts, acids and dusts), whereas temperature profiles are obtained taking into account the heat conduction and diapiric convection models for the Galilean satellites. The combination of electromagnetic and thermal properties of the icy crust, allowed us to generate simulated radar data at the operation frequency of RIME (9 MHz). Such simulations are important to determine the radar performance in the icy crusts, and in particular to estimate the signal penetration and the capability to resolve buried layers.

In order to test the accuracy of Ground Penetrating Radar (GPR) in the detection of subsurface targets for planetary exploration, a laboratory scale experiment is performed based on a ‘sand box’ setup using two different bistatic GPR commercial instruments. Specific attention is paid to the challenging case of buried dielectric scatterers whose location and dimensions are of the same order of magnitude of the GPR antenna separation and signal wavelengths. The target depth is evaluated by using the wave propagation velocity measured with Time Domain Reflectometry (TDR). By means of a proper modeling of the different wave-propagation contributions to the gathered signal, the position of buried targets is correctly estimated with both GPRs even for rather shallow and small-size scatterers in near-field conditions. In this frame, relevant results for a basalt block buried in a silica soil are discussed. The experimental configuration is also simulated with an ad-hoc numerical code, whose synthetic radar sections fully confirm the measured results. The acquired information is of paramount importance for the analysis of various scenarios involving GPR on-site application in future space missions.

"\"In the present paper we combined two different non-destructive techniques to detect the water content spatial variation in a porous material. The main goal of this work was to verify the ability of radar “early time” signals, using the proton density values measured with the unilateral NMR (Nuclear Magnetic Resonance) technique, in order to detect the spatial distribution of water in the subsurface of a concrete slab. This site was chosen because it was the best compromise between an uniform, porous and slow drainage material and the antenna-coupling, affected only by the surface permittivity variations due to the change in water content. The GPR (Ground Penetrating Radar) survey has been conducted using a bistatic radar unit (Sensors & Software, Inc) operating at 1000 MHz; on the other hand, NMR data were collected using portable unilateral NMR operating at 16.3 MHz. The results obtained in this paper confirm that the “early time” radar signal and the NMR response can be applied to estimate some physical properties of both natural and man-made materials. In fact, the data show a matching pattern of the water distribution in the shallow part of the slab measured by GPR and NMR, and a very high correlation coefficient between the radar signal amplitude and the NMR signal integral. Finally, the results highlight the importance of this new combined approach to evaluate different physical parameters at the same time.\""

A spacecraft in orbit around Jupiter's moon Ganimede can use ice penetrating radar to probe for a possible liquid water ocean beneath Ganimede's surface ice. The success of such a mission is constrained to the electromagnetic properties of ice, possible subsurface temperature gradients, and possible impurities in the ice. Several saline ice samples were analyzed using Time Domain Reflectometry technique to extract the electrical permittivity and conductivity as function of temperature, from 20°C to -30°C.

Radar observations from Marsis have demonstrated that Martian Polar Layered Deposits (PLD's) are very transparent to radar waves. Thus, the sounder is able to detect the presence of subsurface reflections in the polar regions below the ice-rich layered deposits. The analysis of radar data makes it possible to gain information about some physical features of Mars surface. In this work an electromagnetic inversion model is used to characterize the shallower structures. This approach assumes that structure consists of layers with parallel plane interfaces and that the electromagnetic properties of the first layer are known a priori. Under these assumptions it is possible to estimate the dielectric permittivity of the subsurface structure. The inversion method has been tested in an area of South Pole and reconstruction results are shown.

Preservation of historical buildings requires particular care, as any intervention must not alter or damage the style, structure or contents of the edifice. In order to properly plan the restoration of a building, non-destructive techniques can be used extensively to detect structural elements and weaknesses. Ground-penetrating radar (GPR) is particularly well adapted to this type of work, as the method is non-invasive, rapid and provides high-resolution images of contrasting subsurface materials. In the present work we show the successful application of the GPR technique to the investigation of two historical buildings that differ in age, structure and geometry. The first case is the GPR detection of fractures and internal lesions in the architrave of the Porticus Octaviae, a partially restored Roman building. The second case uses GPR in the important Zuccari Palace to determine the internal structure above vaulted ceilings that host a series of 16 th century frescos. Both buildings are located in downtown Rome, Italy. These examples show that GPR can give detailed, non-invasive data that describe the state of conservation of historical buildings. In particular, this technique can produce fundamental information for the restorers (e.g., location, dimension and geometry of the structural lesions) that will help them develop the best possible protection plan, retrieving quantitative information about the location and the dimension of the lesions as well as the thickness of the different layers.

An understanding of gas migration along faults is important in many geologic research fields, such as geothermal exploration, risk assessment, and, more recently, the geologic storage of man-made carbon dioxide [Formula: see text]. If these gases reach the surface, they typically are discharged to the atmosphere from small areas known as gas vents. In a study of an individual gas vent located in the extinct Latera caldera, central Italy, near-surface geochemical and geophysical surveys were conducted to define the spatial distribution of gas-induced effects in the first few meters of the soil and, by inference, the 3D structure and geometry of the associated gas-permeable fault. Grid surveys and detailed profiles were performed across this vent using time-domain reflectometry (TDR), ground-penetrating radar (GPR), frequency-domain electromagnetics (FDEM), electrical resistivity tomography (ERT), and gas geochemistry measurements. Detailed profilesurveys indicate that the leaking [Formula: see text] has changed the physical, chemical, and biological soil environment of the vent, resulting in significant spatial variations in parameters (e.g., water content and soil electric/dielectric properties) that influence geophysical measurement results. Despite the strong difference in vertical and lateral resolution and depth of investigation, all methods show the same general trends and similar relative variations in the measured physical parameters. TDR and GPR data highlight anomalous shallow lateral variations, whereas FDEM and ERT measurements identify the vertical extension of the anomalous zone. All methods highlight a north-northwest–south-southeast anomaly alignment that we associate with the main fault; FDEM and, to a lesser extent, [Formula: see text] flux also show elongation orthogonal to this direction, implying that the vent may occur at the intersection of two structures. Thus, different near-surface geophysical and geochemical methods can provide important information on faults and their gas-migration characteristics.

The identification of the physical nature of an object or target causing a ground-penetrating radar (GPR) anomaly, as well as the estimation of a target's dimensions and geometry, is rather challenging. To improve target identification, basic studies are still required, and they can be addressed primarily using a laboratory- or field-based physical model. The field model (test site) is usually expensive and difficult to build, but it provides data for controlled target properties and geometry from a natural environment that are essential for testing processing techniques. In this paper, we present the results from a field experiment where GPR data were collected on plastic and metallic pipes. The main objective is the comparison of the classical migration technique with a microwave tomography approach for reconstructing the geometrical target properties. The use of the microwave tomography approach will allow us to obtain more focused and stable images of the buried objects compared to the ones obtained using classical migration techniques.